According to state-run media KCNA on Tuesday, North Korea warned that any attempt to shoot down one of its test missiles would be viewed as a declaration of war and attributed rising tensions to a joint military drill between the US and South Korea.

Kim Yo Jong, the influential sister of leader Kim Jong Un, said in a statement that Pyongyang would consider it as a “declaration of war” if the U.S. took military action against the North’s strategic nuclear tests.

She also hinted that the North could fire more missiles into the Pacific Ocean. The United States and its allies have never shot down North Korean ballistic missiles, which are banned by the United Nations Security Council, but the question drew new scrutiny since the North suggested it will fire more missiles over Japan.

“The Pacific Ocean does not belong to the dominium of the U.S. or Japan,” Kim said.

Analysts have said that if North Korea follows through on its threat to turn the Pacific Ocean into a “firing range”, it would allow the isolated and nuclear-armed state to make technical advances in addition to signalling its military resolve.

In a separate statement, the chief of the Foreign News Section at North Korea’s Foreign Ministry accused the U.S. of “aggravating” the situation by conducting a joint air drill with a B-52 bomber on Monday and planning U.S.-South Korea field exercises.

In response, South Korea’s Unification Ministry, which handles relations with the North, said Pyongyang’s “reckless nuclear and missile development” is to blame for the deteriorating situation.

The United states deployed the B-52 bomber for a joint drill with South Korean fighter jets, in what South Korea’s defense ministry said was a show of force against North Korea’s nuclear and missile threats.

The two countries will conduct more than 10 days of large-scale military exercises known as the “Freedom Shield” drills starting next week.

According to the Yonhap news agency, U.S. and South Korean jets conducted swift takeoffs on Tuesday as part of a rehearsal in response to North Korean threats to destroy airfields.

The army of North Korea claimed on Tuesday that its adversary fired 30 rounds of artillery from close to the border and demanded an immediate end to such “provocative measures”.

South Korea denied doing so and refuted the assertion.

As a result of the 1950–1953 Korean War, which ended in an armistice rather than a peace treaty and left the two nations formally at war, there are currently about 28,500 American troops stationed in South Korea.